Cellulose microfibrils with modified surface, preparation method and use thereof

ABSTRACT

The invention concerns cellulose microfibrils with modified surface, characterised in that the hydroxyl functions present at the surface of the microfibrils are etherified with at least an organic compound comprising at least a function capable of reacting with said hydroxyl functions, and the degree of surface substitution (DSs) is at least 0.05. The invention also concerns a method for obtaining said microfibrils and their use as agent for modifying viscosity, texture and/or as reinforcing filler.

This application is an application under 35 U.S.C. Section 371 ofInternational Application Number PCT/FR99/02148 filed on Sep. 9, 1999.

A subject-matter of the present invention is cellulose microfibrils witha modified surface, their process of preparation and their use.

Another subject-matter of the invention is compositions comprisingcellulose microfibrils with a modified surface.

Generally, native cellulose is a chain of D-anhydroglucopyranose unitsbonded to one another at the β-1,4 positions. The degree ofpolymerization (DP) of the said chain can vary from a few hundred toseveral thousand monomer units, depending upon the source used. In thenative state, intermolecular hydrogen bonds promote a parallelassociation of the cellulose chains with one another to formmicrofibrils with more or less crystalline structures, the diameter ofwhich can vary from 10 Å to 500 Å.

These microfibrils are well known materials which have already beenproposed, in general, for modifying the rheology of the media into whichthey are introduced.

In the case of fluid aqueous or organic media of the type of thoseintended for the production in particular of cosmetic compositions, ofdrilling fluids, and the like, the microfibrils can modify the viscosityand/or the texture of the medium, indeed even its rheological profile.

In highly viscous and solid media of the type of those intended to beemployed in thermoplastics, thermosetting materials, elastomers andmastics, the microfibrils can modify the mechanical properties and canact in particular as reinforcing filler.

The advantageous mechanical properties of microfibrils are attributed totheir specific structure; they have a highly hydrophilic nature due tothe presence of hydroxyl functional groups at the surface of themicrofibril.

However, the use of these microfibrils is not without disadvantage.

This is because the hydrophilic nature, which may be desirable in someapplications, for example in aqueous and/or hydrophilic media, canconstitute an obstacle to various applications desired in organic and/orhydrophobic media.

For example, in an organic and/or hydrophobic medium, the microfibrilsdo not disperse and phenomena of agglomeration and of flocculationoccur, these phenomena being due to the incompatibility of themicrofibrils with the organic medium in which they are found; as themicrofibrils have a strongly hydrophilic nature, they will naturallyhave a tendency to flocculate and to agglomerate in an organic mediumwith a hydrophobic nature.

As a result of these phenomena, more particularly in an organic medium,the microfibrils will no longer be in a position to exercise their roleof texturizing or viscosifying agent and/or of reinforcing filler.

An aim of the present invention is to provide cellulose microfibrilswhich, while having retained their initial morphological and crystallineaspects and thus all the advantageous mechanical properties which resulttherefrom, exhibit a markedly weakened hydrophilic nature.

Another aim of the invention is to provide microfibrils which can bedispersed in an organic medium.

These aims are achieved by the present invention, the subject matter ofwhich is cellulose microfibrils with a modified surface, characterizedin that the hydroxyl functional groups present at the surface of themicrofibrils are etherified by at least one organic compound comprisingat least one functional group which can react with the said hydroxylfunctional groups and in that the degree of surface substitution (DSS)is at least 0.05.

The organic residues originating from the etherifying organic compoundsattached at the surface of the microfibrils provide for bettercompatibility of the microfibril with the organic medium in which it isdispersed. The hydrophilic nature of the microfibrils is consequentlymarkedly weakened and they can thus control the rheological propertiesof the medium.

At this stage, it is important to define the term “dispersibility”.

In the context of the present invention, the term “dispersibility”denotes the surface-modified microfibrils which, once introduced into anorganic medium, are capable of dispersing with a gentle shearing and offorming a non-flocculating dispersion.

In other words, the microfibrils of the invention are rendereddispersible by a surface hydrophobicization of the hydroxyl functionalgroups: their initial morphology is retained and a crystallinearrangement is still observed.

Within the meaning of the invention, the term “organic medium” denotes amedium composed of an inert organic and/or hydrophobic liquid or of amixture of inert organic and/or hydrophobic liquids in which the“unmodified” microfibrils do not disperse. When it is a mixture ofliquids, they will preferably be miscible. Mention may be made, by wayof indication, of:

alcohols, such as ethanol, isopropanol, butanol, hexanol or octanol;

aldehydes and ketones, such as butyraldehyde, acetone, methyl ethylketone or 4-methyl-2-pentanone;

cyclic or acyclic ethers, such as diethyl ether and its higherhomologues, dioxane or tetrahydrofuran;

halogenated solvents, such as dichloro-, dibromo- or diiodomethane,chloroform, bromoform or carbon tetrachloride;

cyclic or acyclic alkanes, such as pentane, hexane, octane, dodecane,cyclopentane or cyclohexane;

optionally substituted aromatic solvents, such as benzene, toluene,chlorobenzene, bromobenzene;

alkyl acetates, such as methyl acetate, ethyl acetate, propyl acetate,butyl acetate or pentyl acetate;

fatty acid esters, such as isopropyl myristate or the methyl esters ofpalmitic acid, stearic acid, arachidic acid, soybean oil fatty acid,rapeseed oil fatty acid, maize oil fatty acid, sunflower oil fatty acidor groundnut oil fatty acid.

The cellulose microfibrils can be of any origin, for example of plant,bacterial, animal, fungal or amoebic origin, preferably plant, bacterialor animal origin.

Mention may be made, as an example of animal sources of cellulose, ofanimals of the Tunicata.

The plant sources of cellulose can be wood, cotton, flax, ramie, certainalgae, jute, sugarbeet pulp or citrus fruits (lemon, orange orgrapefruit) or the like.

Whatever the origin of the microfibrils, they advantageously exhibit anL/D ratio of greater than 15, advantageously of greater than 50, moreparticularly of greater than 100 and preferably of greater than 500 anda mean diameter (D) of between 10 Å and 500 Å, advantageously between 15Å and 200 Å, more particularly between 15 Å and 70 Å, preferably between18 Å and 40 Å, L representing the length of the microfibrils and D theirmean diameter.

The microfibrils can be obtained from the abovementioned cellulosesources by various processes already described in the literature.Reference may be made, among these processes, for example to theprocesses disclosed in European Patent Applications EP 0 726 356 and EP0 102 829 or U.S. Pat. No. 4,481,076, the teachings of which on thissubject are incorporated here.

According to a particularly advantageous embodiment of the presentinvention, the microfibrils are obtained by employing the process whichwill be described below.

More particularly, this process is carried out on pulp from plants withprimary walls, such as, for example, beet pulp after the latter has beensubjected to a stage of preliminary extraction of the sucrose, accordingto methods known in the art.

Thus, the process comprises the following stages:

(a) first acidic or basic extraction, on conclusion of which a firstsolid residue is recovered,

(b) optionally, second extraction, carried out under alkalineconditions, of the first solid residue, following which a second solidresidue is recovered,

(c) washing of the first or second solid residue,

(d) optionally, bleaching of the washed residue,

(e) dilution of the first solid residue obtained on conclusion of stage(d), so as to obtain a solids content of between 2 and 10% by weight,

(f) homogenization of the dilute suspension.

In stage (a), the term “pulp” is understood to mean wet, dehydrated pulppreserved by ensiling or partially depectinized.

The extraction stage (a) can be carried out in an acidic medium or in abasic medium.

For an acidic extraction, the pulp is suspended in an aqueous solutionfor a few minutes, so as to homogenize the acidified suspension at a pHof between 1 and 3, preferably between 1.5 and 2.5.

This operation is carried out with a concentrated solution of an acid,such as hydrochloric acid or sulphuric acid.

This stage can be advantageous in removing calcium oxalate crystalswhich may be present in the pulp and which, because of their highlyabrasive nature, can result in difficulties in the homogenization stage.

For a basic extraction, the pulp is added to an alkaline solution of abase, for example sodium hydroxide or potassium hydroxide, with aconcentration of less than 9% by weight, more particularly of less than6% by weight. The concentration of the base is preferably between 1 and2% by weight.

The small amount of a water-soluble antioxidizing agent, such as sodiumsulphite Na₂SO₃, can be added in order to limit the oxidation reactionsof the cellulose.

Stage (a) is generally carried out at a temperature of betweenapproximately 60° C. and 100° C., preferably of between approximately70° C. and 95° C.

The duration of stage (a) is between approximately 1 hour andapproximately 4 hours.

During stage (a), partial hydrolysis takes place with release andsolubilization of most of the pectins and hemicelluloses, whileretaining the molecular mass of the cellulose.

The solid residue is recovered from the suspension originating fromstage (a) by employing known methods. Thus, it is possible to separatethe solid residue by centrifugation, by filtration under vacuum or underpressure, with filter cloths, or filter presses, for example, or byevaporation.

The first solid residue obtained is optionally subjected to a secondextraction stage carried out under alkaline conditions.

A second extraction stage, stage (b), is carried out when the first hasbeen carried out under acidic conditions. If the first extraction wascarried out under alkaline conditions, the second stage is onlyoptional.

According to the process, this second extraction is carried out with abase preferably chosen from sodium hydroxide and potassium hydroxide,the concentration of which is less than approximately 9% by weight,preferably of between approximately 1% and approximately 6% by weight.

The duration of the alkaline extraction stage is between approximately 1and approximately 4 hours. It is preferably equal to approximately 2hours.

On conclusion of this second extraction, if it takes place, a secondsolid residue is recovered.

In stage (c), the residue originating from stage (a) or (b) is copiouslywashed with water in order to recover the cellulose material residue.

The cellulose material from stage (c) is then optionally bleached, instage (d), according to conventional methods. For example, a treatmentwith sodium chlorite, with sodium hypochlorite or with hydrogen peroxidein a proportion of 5-20% with respect to the amount of solids treatedcan be carried out.

Various concentrations of bleaching agent can be used, at temperaturesof between approximately 18° C. and 80° C., preferably betweenapproximately 50° C. and 70° C.

The duration of this stage (d) is between approximately 1 hour andapproximately 4 hours, preferably between approximately 1 andapproximately 2 hours.

A cellulose material comprising between 85 and 95% by weight ofcellulose is then obtained.

On conclusion of this bleaching stage, it may be preferable to copiouslywash the cellulose with water.

The resulting suspension, optionally bleached, is subsequently redilutedin water in a proportion of 2 to 10% of solids (stage (e)), before beingsubjected to a homogenization stage (stage (f)) comprising at least onecycle.

The homogenization stage corresponds to a mixing or milling operation orany operation of high mechanical shear, followed by one or more passesof the suspension of cells through an orifice with a small diameter,subjecting the suspension to a drop in pressure of at least 20 mPa andto a high-speed shear action, followed by a high-speed decelerationimpact.

The mixing or milling is carried out, for example, by pass(es) throughthe mixer or mill for a period of time ranging from a few minutes toapproximately one hour in a standard device, such as a Waring Blenderequipped with a four-blade propeller, or edge runner mill or any othertype of mill, such as a colloid mill.

The homogenization proper will advantageously be carried out in ahomogenizer of the Manton Gaulin type in which the suspension issubjected to a shear action at high speed and high pressure in a narrowpassage and against an impact ring.

Mention may also be made of the Micro Fluidizer, which is a homogenizermainly composed of a compressed-air motor which will create very highpressures, of an interaction chamber, in which the homogenizationoperation (elongational shear, impacts and cavitations) will take place,and of a low-pressure chamber which allows the dispersion to bedepressurized.

The suspension is introduced into the homogenizer, preferably afterpreheating to a temperature of between 40 and 120° C., preferably ofbetween 85 and 95° C.

The temperature of the homogenization operation is maintained between 95and 120° C., preferably above 100° C.

The suspension is subjected, in the homogenizer, to pressures of between20 and 100 mPa and preferably of greater than 50 mPa.

The homogenization of the cellulose suspension is obtained by a numberof passes which can vary between 1 and 20, preferably between 2 and 5,until a stable suspension is obtained.

The homogenization operation can advantageously be followed by anoperation of high mechanical shear, for example in a device such as theUltra Turrax from Silverson.

Once obtained, the microfibrils will be subjected to an etherificationreaction.

In the context of the present invention, the term “etherification” isemployed in the broad sense and denotes reactions in which hydroxylfunctional groups O—H can be converted into O—Y, in particular:

silylation reactions (Y=—SiR₁R₂R₃),

etherification reactions (Y=—R₄),

condensations with isocyanates (Y=—CO—NH—R₅),

condensations or substitutions with alkylene oxides (Y=CH₂—CH(R₆)—OH),

condensations or substitutions with glycidyl compounds(Y=—CH₂—CH(OH)—CH₂—R₇).

The organic compound comprising at least one functional group which canreact with the hydroxyl functional groups which are found at the surfaceof the microfibrils will also be referred to, in the continuation of theaccount, as etherifying organic compound or etherification agent.

The etherification agent is advantageously chosen from silylatingagents, isocyanates, halogenated alkylating agents, alkylene oxidesand/or glycidyl compounds.

The silylating agents can be chosen from:

haloalkylsilanes of formula: R₃R₂R₁Si—X, R₂R₁Si(X)₂ or R₁Si(X)₃;

disilazanes of formula: R₃R₂R₁N—Si—NR₁R₂R₃;

N-silylacetamides of formula: CH₃—CO—NH—SiR₁R₂R₃; and

alkoxysilanes of formula: R₃R₂R₁Si—OR or R₂R₁Si (OR) (OR₃);

in which

R, R₁, R₂ and R₃, which are identical or different, can be chosen fromoptionally substituted, saturated or unsaturated, linear, branched orcyclic hydrocarbonaceous radicals comprising from 1 to 30 carbon atoms,and

X is a halogen atom chosen from chlorine, bromine or iodine.

The R, R₁, R₂ and R₃ radicals can be chosen from methyl, ethyl, propyl,isopropyl, butyl, sec-butyl, tert-butyl, pentenyl, hexyl, cyclohexyl,octyl, nonyl, decyl, dodecyl, undecyl, nonadecyl, eicosyl (C₂₀), docosyl(C₂₂), octacosyl (C₂₈), triacontanyl (C₃₀), vinyl, allyl, phenyl, styrylor naphthyl.

Mention may more particularly be made, as silylating agent, of:

among haloalkylsilanes: chlorodimethylisopropylsilane,chlorodimethylbutylsilane, chlorodimethyloctylsilane,chlorodimethyldodecylsilane, chlorodimethyloctadecylsilane,chlorodimethylphenylsilane, chloro-(1-hexenyl)dimethylsilane,dichlorohexylmethylsilane, dichloroheptylmethylsilane ortrichlorooctylsilane;

among disilazanes: hexamethyldisilazane,1,3-divinyl-1,1,3,3-tetramethyldisilazane,1,3-divinyl-1,3-diphenyl-1,3-dimethyldisilazane,1,3-N-dioctyltetramethyldisilazane, diisobutyltetramethyldisilazane,diethyltetramethyldisilazane, N-dipropyltetramethyldisilazane,N-dibutyltetramethyldisilazane or1,3-di(para-tertbutylphenethyl)tetramethyldisilazane;

among N-silylacetamides; N-trimethylsilylacetamide,N-methyldiphenylsilylacetamide or N-triethylsilylacetamide;

among alkoxysilanes: tert-butyldiphenylmethoxysilane,octadecyldimethylmethoxysilane, dimethyloctylmethoxysilane,octylmethyldimethoxysilane, octyltrimethoxysilane, trimethylethoxysilaneor octyltriethoxysilane.

The hydroxyl functional groups of the microfibrils can also beetherified by halogenated alkylating agents of formula R₄—X, in which Xis a halogen atom chosen from chlorine, bromine and iodine, and R₄ is ahydrocarbonaceous radical corresponding to the same definition as R, R₁,R₂ and R₃.

Mention may more particularly be made, among halogenated alkylatingagents, of:

chloropropane or chlorobutane;

bromopropane, bromohexane or bromoheptane, and

iodomethane, iodoethane, iodooctane, iodooctadecane or iodobenzene.

The etherification agent can, in addition, be an isocyanate of formulaR₅—NCO, in which R₅ is a hydrocarbonaceous radical corresponding to thesame definition as R, R₁, R₂ and R₃.

The isocyanate is advantageously chosen from butyl isocyanate,tert-butyl isocyanate, pentyl isocyanate, octyl isocyanate, dodecylisocyanate, octadecyl isocyanate or phenyl isocyanate.

Alkylene oxides can also be used as etherification agent. In thealkylene oxides of formula:

R₆ can represent a hydrocarbonaceous radical corresponding to the samedefinition as R, R₁, R₂ and R₃.

Mention may be made, by way of examples, of 1,2-epoxybutane,1,2-epoxyhexane, 1,2-epoxyoctane, 1,2-epoxydecane, 1,2-epoxydodecane,1,2-epoxyhexadecane, 1,2-epoxyoctadecane or 1,2-epoxy-7-octene.

The etherification agent can also be a glycidyl compound of formula:

in which R₇ can represent a hydrocarbonaceous radical corresponding tothe same definition as R, R₁, R₂ and R₃.

More particularly, the glycidyl compound can be chosen from methylglycidyl ether, propyl glycidyl ether, butyl glycidyl ether,2-methylbutyl glycidyl ether, ethylhexyl glycidyl ether, octyl glycidylether, lauryl glycidyl ether, allyl glycidyl ether or benzyl glycidylether.

The hydroxyl functional groups of the microfibrils can be etherifiedwith a single type of etherification agent among those mentioned aboveor with etherification agents of different natures.

In the case of an etherification by agents of different natures, theetherification can take place either in one or in several successivereaction(s), which would result in the production of microfibrilscomprising different organic residues at the surface.

One of the essential characteristics of the surface-modifiedmicrofibrils is their degree of surface substitution (DSS).

The degree of surface substitution (DSS) is generally defined as thenumber of surface hydroxyl functional groups substituted per glucoseunit. It is obtained from the overall mean degree of substitution DSfrom the general formula:

(DSS)−(DS)/(Cs/Ct)

in which Cs represents the surface chains and Ct represents the totalchains.

The overall mean DS is obtained by the determination of theconcentration by weight of all or part of the group grafted by theetherification reaction and by applying the following general formula:

DS=(162×Y)/[(g×100)−(G×Y)]

in which

Y represents the percentage by weight with respect to the total weightof the grafted product of the part analysed (which can thus be the % w/wof a heteroatom, measured by elemental analysis, or alternatively the %w/w of a group, measured by a chromatographic technique),

g represents the molecular weight of the part analysed (in the case of aheteroatom, it will be the atomic weight of this heteroatom; in the caseof a given group, it will be the molecular weight of the group),

G represents the total molecular weight of the group grafted byetherification.

The degrees of surface substitution (DSS) calculated below make possiblea better understanding of this method of determination.

Calculation of the (DSS) for silylating agents:

In the case where the surface hydroxyl groups of the microfibrils aremodified by a silylating agent, for example a haloalkylsilane, inparticular chlorodimethylisopropylsilane, the substitution of nhydrogens by n alkylsilane groups, in particular dimethylisopropylsilyl,results in the following empirical formula of the final compound:

C_((6+5n))H_((10+12n))Si_(n)O₅

with a molar mass M=162+100n; 162 being the molar mass of a hexose unit.The percentage of silicon will thus be:${\% \quad {Si}} = {y = {\frac{28\quad n}{162 + {100n}} \times 100}}$

from which it is possible to obtain the overall degree of substitution(DS), which will then be: ${DS} = \frac{162y}{2800 - {100y}}$

The degree of surface substitution (DSS) is subsequently obtained fromthe ratio of the Cs (number of surface chains) to the Ct (total numberof chains):

(DSS)=(DS)/(Cs/Ct)

as the ratio Cs/Ct is 0.77 in the case of beet microfibrils, the (DSS)will then be equal to:

(DSS)=(DS)/0.77

Calculation of the (DSS) for isocyanate reactants:

In the case of the modification of the surface hydroxyl groups of thecellulose microfibrils by an isocyanate reactant as defined above, thesubstitution of n hydrogens by n alkylurethane groups, for exampleoctylurethane, the empirical formula of the final compound will be asfollows:

 C_((6+9n))H_((10+17n))N_(n)O_((5+n))

corresponding to a molar mass M=162+155n; 162 being the molar mass of ahexose unit.

The percentage of nitrogen will thus be:${\% \quad N} = {y = {\frac{14n}{162 + {155n}} \times 100}}$

from which it is possible to obtain the overall degree of substitution(DS): ${DS} = \frac{162y}{1400 - {155y}}$

The degree of surface substitution (DSS) is subsequently obtained fromthe ratio of the Cs (number of surface chains) to the Ct (total numberof chains), which is 0.77 in the case of beet microfibrils:

(DSS)=(DS)/0.77

Calculation of the (DSS) for halogenated alkylating agents, alkyleneoxides or glycidyl compounds: The substitution of n hydrogens of thesurface hydroxyl groups of the cellulose microfibrils by n alkyl groupsoriginating from a haloalkyl, such as butyl originating, for example,from chlorobutane, results in an empirical formula of the final compoundwhich will be:

C_((6+4n))H_((10+8n))O₅

corresponding to a molar mass M=162+56n; 162 being the molar mass of ahexose unit.

If y % by weight of butyl (C₄H₉) unit is quantitatively determined withrespect to the starting material, the overall DS will be obtained withthe following formula:${DS} = {\frac{162y}{56} \times \frac{1}{100 - \quad y}}$

To obtain the (DSS), it is necessary, as above, to use the formula:

(DSS)=(DS)/(Cs/Ct)

When the etherification agent is a silylating agent or an isocyanate,the degree of surface substitution can be determined by conventionalelemental analysis.

In the case where the etherification is carried out by halogenatedalkylating agents, alkylene oxides or glycidyl compounds, the (DSS) canbe determined by quantitative determination of the alkyl groups,advantageously according to the Zeisel method described in AnalyticalChemistry No. 13, p. 2172, 1979. This method consists in decomposing theether bond at 140° C. in the presence of hydrogen iodide (HI) and inquantitatively determining the corresponding iodides by gaschromatography.

The alkyl groups can also be determined by ¹³C nuclear magneticresonance according to the method described by Y. Tezuka: Determinationof substituent distribution in cellulose ether by mean of ¹³C NMR studyon their acetylated derivatives, Makromol. Chem., 191, p. 681, 1990.

The degree of surface substitution (DSS) is at least 0.05,advantageously between 0.1 and 1 and more particularly between 0.2 and0.7.

Another subject-matter of the invention is a process for the manufactureof cellulose microfibrils with a modified surface, such as have beendescribed above, from cellulose microfibrils obtained by fibrillation ofa material comprising cellulose fibres, characterized in that itconsists in:

i—wetting and/or dispersing the cellulose microfibrils in a liquidmedium which does not destroy the cellulose microfibril,

ii—adding, to the dispersion, an agent for the etherification or amixture of agents for the etherification of the hydroxyl functionalgroups of the cellulose and optionally a catalyst and/or an activator ofthe etherification reaction,

iii—halting the etherification reaction after the desired degree ofsurface substitution (DSS) has been obtained,

iv—separating the microfibrils thus obtained from the reaction medium.

The term “medium which does not destroy the cellulose microfibril” isunderstood to mean a medium in which the microfibril retains its nativecrystalline nature.

Thus, the microfibrils are first dispersed in a liquid medium—stage (i).

This liquid should advantageously not dissolve the cellulose nor have anegative effect on the structure of the cellulose microfibrils.

Mention may be made, as suitable liquids, of aliphatic and/or cyclicethers, in particular ethyl ether and tetrahydrofuran; optionallyhalogenated aliphatic hydrocarbons, in particular hexane, xylene orperchloroethylene; optionally halogenated aromatic hydrocarbons, inparticular toluene or pyridine; alcohols, in particular isopropanol orbutanol; and water; it being possible for these liquids to be alone oras a mixture.

After dispersion of the microfibrils, in stage (ii), an etherificationagent or mixture of etherification agents is added to the medium,advantageously with an etherification catalyst and/or activator.

The etherification agents are chosen from those described above.

The etherification catalysts can be chosen from the group comprising,for example, imidazole, pyridine, triethylamine, tetrabutylammoniumfluoride hydrate, trimethylsilyl chloride, sodium hydroxide, potassiumhydroxide or tin derivatives, such as, for example, tin octanoate or tindilaurate.

Mention may be made, as activating agent for the reaction for theetherification of the cellulose microfibrils, by way of examples, ofsodium hydroxide, potassium hydroxide or pyridine.

According to the choice of the etherifying organic compound(s), a personskilled in the art will know how to choose the catalyst and/or theactivator which is/are the best suited and their concentration(s), bothwith respect to the dispersing liquid medium and with respect to themicrofibrils.

The nature and the concentration of the catalyst and/or of the activatorwill be chosen so as to avoid destroying the microfibril.

According to a specific embodiment, stages (i) and (ii) can optionallybe concomitant.

The etherification reaction is advantageously carried out with stirringand optionally in an inert atmosphere.

The etherification reaction is carried out at the appropriatetemperature for a period of time determined according to the degree ofsurface substitution (DSS) desired. The temperature will be chosen whiletaking into account the nature of the therification agent and itsreactivity.

The halting of the etherification—stage (iii)—is achieved, for example,either by addition of a compound, advantageously water, which rendersthe etherification agent inactive or by cooling and/or diluting themedium or by exhaustion of the etherification agent or agents.

The partially etherified microfibrils are then extracted from themedium—stage (iv)—by any appropriate means, in particular bylyophilization, centrifugation, filtration or precipitation.

The microfibrils are then advantageously washed and dried.

When it is desired to manufacture microfibrils which are modified at thesurface by different organic residues, either the operations describedabove are repeated while adding, in stage (ii), a differentetherification agent on each occasion or the dispersion of microfibrilsis treated in stage (ii) with a mixture of etherification agents.

This principle also applies when stages (i) and (ii) are concomitant.

The surface modification of the microfibrils thus makes it possible toobtain a very good dispersibility and compatibility with organic media,whether they are fluid, highly viscous or solid.

Another subject-matter of the invention relates to the use of thesurface-modified microfibrils in accordance with the invention asviscosifying and/or texturizing agents for fluid media and/or astexturizing agent and/or reinforcing filler for highly viscous or solidmedia.

They can be employed in the pulverulent form or in the form of anorganic dispersion.

A further subject-matter of the present invention is compositionscomprising cellulose microfibrils with a modified surface such as havebeen described above or such as have been obtained according to theabovementioned process.

The microfibrils of the invention can exercise their role ofviscosifying agents in cosmetic formulations, drilling fluids, paints,glazes, adhesives or inks and as reinforcing filler in polymers, inparticular in thermoplastics, thermosetting materials, crosslinked ornoncrosslinked elastomers, and mastics.

Another subject-matter of the present invention is compositionscomprising microfibrils with a modified surface such as have beendescribed above or such as have been obtained according to theabovementioned process.

It is possible to add to these compositions, in addition to themicrofibrils, the usual additives necessary for their use according tothe field of application, such as, for example, vulcanizationingredients in the specific case of elastomers, coupling agents,plasticizers, stabilizers, lubricants, pigments, and the like.

These compositions can be employed, for example, as floor coverings,engine mounts, components of vehicle tracks, shoe soles, cablewaywheels, seals for domestic electrical appliances, cable sheaths ortransmission belts.

Finally, the compositions according to the invention can findapplications as battery separator.

Thus, the present invention makes it possible to obtain compositionsbased on an elastomer or an alloy or blend of elastomers, the elastomerpreferably being vulcanized, which can be used in any part of the tyre.

In this specific case, it should be noted that the content ofassociation according to the invention is such that the content ofmicrofibrils in the concerned part of the tyre can range up to 80% byweight, more particularly can be between 0.1 and 50% by weight, withrespect to the total weight of the composition.

In the other applications, lower contents of microfibrils may bedesired. It is possible, for example, to envisage compositionscomprising at most 10% by weight, advantageously at most 5% by weightand preferably at most 2% by weight with respect to the total weight ofthe composition.

The following examples illustrate the invention without, however,limiting the scope thereof.

EXAMPLES Example 1 Etherification of the Microfibrils byChlorodimethylisopropylsilane

Approximately 10 g of an aqueous suspension of parenchyma cellulosemicrofibrils (with a concentration equal to 2.3% as weight/weight) areplaced in a centrifuge tube with a capacity of 100 cc, to whichapproximately 80 cc of acetone are subsequently added.

The mixture is then centrifuged for 30 minutes at 3 700 rev/min. Thepellet obtained is resuspended in acetone and then centrifuged to removethe solvent. The latter operation is repeated: 3 times with acetone,once with an acetone/methanol (50/50 v/v) mixture, twice with tolueneand a final time with anhydrous toluene. The final pellet is recoveredand suspended in 10 ml of anhydrous toluene.

Following this operation, on the one hand, the solids content isdetermined by drying and weighing and, on the other hand, the residualwater content is determined by Karl Fischer quantitative determination(device equipped with a Büchi oven heated to 150° C. for 1 hour whileflushing with nitrogen).

In this example, the amount of cellulose is 0.158 g (0.975×10⁻³ mol) ofanhydroglucose equivalent and the water content is 0.0181 g (1.0×10⁻³mol).

The suspension is then placed in a reactor and the desired amount ofreactant is added so as to have 2 mol of silane per 1 surfaceanhydroglucose group.

0.40 ml of chlorodimethylisopropylsilane, with a molecular weight of136.7 and a relative density of 0.869, and 0.174 g of imidazole(2.55×10⁻³ mol) are thus added.

The mixture is then stirred in the closed reactor at ambient temperaturefor 16 hours.

Subsequently, 70 ml of a THF/methanol (80/20 v/v) mixture are added todissolve the salt formed by the reaction between the imidazole and thehydrochloric acid given off during the reaction and to destroy theresidual chlorosilane.

The combined mixture is then centrifuged and the pellet is washed twicewith THF and isolated by centrifugation.

Quantitative Determination of Silicon—Determination of the (DSS)

In order to be able to determine the (DSS) of the microfibrils, thesilicon has to be quantitatively determined. To do this, a fraction ofthe product is treated, prior to this quantitative determination, in aSoxhlet for 48 hours in THF to completely remove the dimers formed. Thesample is subsequently decomposed by combustion in a Schoniger flask,then displaced with an N/10 aqueous NaOH solution and quantitativelydetermined by ICP/AES.

The analysis of the silicon content gives a value of 4.1%, which resultsin a DSS of 0.36.

Observation under a microscope indicates that the microfibrils thus“etherified” still exist in the form of fibres.

The latter flocculate in an aqueous medium but are dispersible in THF.

Example 2 Rheological Behaviour

The rheological behaviour of the suspensions in THF of the microfibrilsobtained in Example 1 was studied.

Measurements are carried out on suspensions with a concentration of 0.1%weight/weight.

The viscosity ( ) is measured on an RFS 8400 rheometer in Couettegeometry (scanning at a shear rate between 0.1 and 100 s⁻¹).

It is expressed in mPa s, it being known that that of the THF is 1mPa·s.

The results are summarized in Table I.

TABLE I at 0.1 sec⁻¹ at 1 sec⁻¹ at 10 sec⁻¹ at 63.9 sec⁻¹ 475 90 19 7.1

It is found that the suspensions of microfibrils of Example 1 in THFexhibit high viscosities and a behaviour of pseudoplastic type (decreasein viscosity when the shear rate increases). This type of behaviour iscomparable with that of the non-surface-modified microfibrils in water.

Example 3 Etherification of the Microfibrils byChlorodimethylisopropylsilane

Approximately 5 liters of acetone are added to one litre of aqueoussuspension of parenchyma cellulose microfibrils (with a concentrationequal to 2.3%). This mixture, which results in the flocculation of thecellulose microfibrils, is subsequently filtered so as to remove themost solvent. The operation is repeated: 3 times with acetone, once withan acetone/toluene (50/50 v/v) mixture, twice with toluene and one finaltime with anhydrous toluene. The medium is homogenized after eachexchange.

The final cake is subsequently recovered and suspended in 1.5 liters ofanhydrous toluene.

The amount of solids is 19.5 g (0.120 mol) and the amount of residualwater is 0.195 g (0.0108 mol).

The suspension is then placed in a reactor and the desired amount ofreactants is added so as to have 1.74 mol of silane per 1 surfaceanhydroglucose group.

27 ml of chlorodimethylisopropylsilane (0.172 mol) and 16 g of imidazoleare thus added.

The mixture is then stirred in the closed reactor at ambient temperaturefor 16 hours.

After reaction, 2 liters of methanol are introduced to dissolve the saltformed by the reaction between the imidazole and the hydrochloric acidgiven off during the reaction and to destroy the residual chlorosilane.

The solvent is removed by filtration and the filtration cake is washedtwice in succession with 2 liters of acetone to remove the silyl etherformed.

The cake is placed in water, the residual acetone is removed on a rotaryevaporator and lyophilization is carried out.

The analysis of the silicon content gives a value of 9%, which resultsin a DSS of 1.

Observation under a microscope shows that the product still exists inthe form of microfibrils.

The microfibrils thus modified form dispersions at ambient temperaturefor a concentration of 0.05% w/w, obtained directly by mixing betweenthe powder and the liquid and then treated for 2 minutes in anultrasonic bath, which dispersions do not flocculate in the followingsolvents:

toluene

diethyl ether

methyl, ethyl, propyl, isobutyl, butyl and pentyl acetate

chloroform, dichloromethane

tetrahydrofuran

1-butanol, 1-hexanol, 1-octanol

butyraldehyde and isophorone

rapeseed oil and isopropyl myristate

silicone oil 48 V 750

Example 4 Etherification of the Microfibrils byChlorodimethylbutylsilane

In this example, the procedure of Example 1 is repeated, in whichprocedure the silylating agent is replaced by chlorodimethylbutylsilane.

The molecular weight of chlorodimethylbutylsilane is 150.7 and itsrelative density is 0.875.

The amount of cellulose in this example is 0.115 g (0.709×10⁻³ mol) ofanhydroglucose (AHGU) equivalent and the water content is 0.0096 g(0.533×10⁻³ mol).

The amount of chlorodimethylbutylsilane is 0.18 ml and that of imidazoleis 0.074 g (1.08×10⁻³ mol).

When the suspension of cellulose in anhydrous toluene is placed in thereactor, the desired amount of silylating agent is added so as to have 1mol of silane per 1 surface anhydroglucose group.

The analysis of the silicon contents gives a value of 1.9%, whichresults in a DSS of 0.155.

Observation under a microscope shows that the microfibrils thus“etherified” still exist in the form of fibrils.

The latter flocculate in an aqueous medium but are dispersible in THF.

Example 5 Etherification of the Microfibrils byChlorodimethyloctylsilane

In this example, the procedure of Example 1 is repeated, in whichprocedure the silylating agent is replaced by chlorodimethyloctylsilane.

The molecular weight of chlorodimethyloctylsilane is 206.8 and itsrelative density is 0.873.

The amount of cellulose in this example is 0.213 g (1.315×10⁻³ mol) ofanhydroglucose (AHGU) equivalent and the water content is 0.017 g(0.944×10⁻³ mol).

The amount of chlorodimethyloctylsilane is 0.70 ml and that of imidazoleis 0.202 mg (3×10⁻³ mol).

When the suspension of cellulose in anhydrous toluene is placed in thereactor, the desired amount of silylating agent is added so as to have 2mol of silane per 1 surface anhydroglucose group.

The analysis of the silicon content gives a value of 5.2%, which resultsin a DSS of 0.57.

Observation under a microscope shows that the microfibrils thus“etherified” still exist in the form of fibres.

The latter flocculate in an aqueous medium but are dispersible in THF.

Example 6 Etherification of the Microfibrils byChlorodimethyldodecylsilane

In this example, the procedure of Example 1 is repeated, in whichprocedure the silylating agent is replaced bychlorodimethyldodecylsilane.

The molecular weight of chlorodimethyldodecylsilane is 262.9 and itsrelative density is 0.865.

The amount of cellulose in this example is 0.177 g (1.092×10⁻³ mol) ofanhydroglucose (AHGU) equivalent and the water content is 0.02 g(1.111×10⁻³ mol).

The amount of chlorodimethyldodecylsilane is 0.85 ml and that ofimidazole is 0.190 mg (2.8×10⁻³ mol).

When the suspension of cellulose in anhydrous toluene is placed in thereactor, the desired amount of silylating agent is added so as to have 2mol of silane per 1 surface anhydroglucose group.

The analysis of the silicon content gives a value of 4.2%, which resultsin a DSS of 0.48.

Observation under a microscope shows that the microfibrils thus“etherified” still exist in the form of fibres.

The latter flocculate in an aqueous medium but are dispersible in THF.

Example 7 Etherification of the Microfibrils by Octyl Isocyanate

In this example, the surface of the microfibrils is modified by reactionof the surface hydroxyl groups with octyl isocyanate.

The first part, corresponding to the exchange of solvent between thewater and the toluene, is identical to that in Example 1.

The suspension of microfibrils in anhydrous toluene comprises 0.167 g ofcellulose (1.03×10⁻³ mol).

It is then placed in a reactor and 1.2 ml of octyl isocyanate, with amolecular weight of 155.2 and a relative density of 0.88, are added.

The mixture is then stirred in the closed reactor at 80° C. for 16hours.

After cooling, 70 ml of methanol are added. The combined mixture is thencentrifuged and the pellet is washed twice with THF and then withhexane.

The analysis of the nitrogen content gives a value of 1.38%, whichresults in a DSS of 0.25.

Observation under a microscope shows that the product still exists inthe form of fibres.

The latter are dispersible in THF.

Example 8 Use in a Crosslinked (Vulcanized) Elastomer

The object of this example is to evaluate the properties of thevulcanized elastomer comprising the modified microfibrils resulting fromExample 3 (composition B), compared with those of an elastomer notcomprising modified microfibrils (composition A).

The following two elastomer compositions are prepared:

A (reference) B (invention) SBR (*) 90.1 73.5 Modified microfibrils —18.4 Antioxidant (**) 1.3 1.06 Stearic acid 2.25 1.84 Zinc oxide 2.251.84 Diphenylguanidine 1.35 1.10 Sulphenamide (***) 1.8 1.47 Sulphur 0.90.73 The amounts are expressed as per cent by weight with respect to thetotal weight of the composition. (*) Styrene-butadiene copolymersynthesized in solution (SBR Buna VSL 5525-1/Bayer) comprising 27.3% ofoil. (**) Antioxidant:N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine. (***) Sulphenamide:N-cyclohexyl-2-benzothiazole-sulphenamide.

Each composition is prepared by applying thermomechanical work in aBrabender internal mixer with a capacity of 70 cm³, in one stage, for amean blade speed of 50 revolutions per minute, until a temperature of100° C. is achieved at the end of the stage, followed by a stage ofacceleration and of finishing on an external mixer. The vulcanization ofthe compositions is adjusted to the kinetics of vulcanization of eachblend.

The physical properties of the blends are recorded in Table II below.

TABLE II Properties A (reference) B (invention) 10% Modulus (MPa) 0.130.2 100% Modulus (MPa) 0.45 0.7 300% Modulus (MPa) 0.92  1.24 Elongation356% 474% Tensile strength (MPa) 1.2  2.1 Shore A 15 s 22    31  

The measurements are carried out according to the following methods:

tension: the moduli are measured on the vulcanizates according toStandard NF T46002. It should be noted that the 10%, 100% or 300%modulus in the rubber trades refers to the stress measured at a tensileelongation of 10%, 100% or 300% respectively.

Shore A 15 s hardness: the Shore A 15 s hardness is measured accordingto Standard ASTM D2240; the value under consideration is determined 15seconds after the application of the force.

From Table II, it is found that the composition comprising thesurface-modified microfibrils (composition B) results in mechanicalstresses and in hardnesses which are markedly higher in comparison withthe reference composition (composition A).

It is noteworthy to observe that the increase in modulus of thecomposition comprising the microfibrils of the invention takes placewithout harming the tensile strength and the elongation at break of thevulcanized composition. On the contrary, in the presence of themicrofibrils, a significant increase in the elongation at break isobserved.

This example clearly shows that the microfibrils with a modified surfacewere homogeneously dispersed in the elastomer. For this reason, theyresult in a significant improvement in terms of mechanical properties incomparison with the reference.

What is claimed is:
 1. Cellulose microfibrils with a modified surface,having hydroxyl functional groups present at the surface etherified byat least one organic compound comprising at least one functional groupwhich reacts with said hydroxyl functional groups and with a degree ofsurface substitution (DSS) of at least 0.05, said organic compound beinga silylating agent, isocyanate, halogenated alkylating agent, alkyleneoxide, or glycidyl compound.
 2. Microfibrils according to claim 1,wherein the silylating agent is: a haloalkylsilane of formula:R₃R₂R₁Si—X, R₂R₁Si(X)₂ or R₁Si(X)₃; a disilane of formula:R₃R₂R₁N—Si—NR₁R₂R₃; a N-silylacetamide of formula: CH₃—CO—NH—SiR₁R₂R₃;or a alkoxysilane of formula: R₃R₂R₁Si—OR or R₂R₁Si(OR)(OR₃);  wherein:—R, R₁, R₂ and R₃, which are identical or different, are optionallysubstituted, saturated or unsaturated, linear, branched or cyclichydrocarbonaceous radicals having 1 to 30 carbon atoms, and —X ischlorine, bromine or iodine.
 3. Microfibrils according to claim 2, whernthe R, R₁, R₂ and R₃ radicals are methyl, ethyl, propyl, isopropylbutyl, sec-butyl tert-butyl, pentenyl, hexyl cyclohexyl octyl, nonyl,decyl dodecyl, undecyl, nonadecyl, eicosyl (C₂₀), docosyl (C₂₂),octacosyl (C₂₈), triacontanyl (C₃₀), vinyl, allyl, phenyl, styryl ornaphthyl.
 4. Microfibrils according to claim 3, wherein the silylatingis chlorodimethylisopropylsilane, chlorodimethylbutylsilane,chlorodimethyloctylsilane, chlorodimethyldodeyilane,chlorodimethyloctadecylsilane, chlordimethylphenylsilane,chloro-(1-hexenyl)dimethylsilane, dichlorohexylmethylsilane,dichloroheptylmethylsilane, trichlorooctylsilane; hexamethyldisilazane,1,3-divinyl-1,1,3,3-tetramethyldisilazane,1,3-divinyl-1,3-diphenyl-1,3-dimethyldisilazane,1,3-N-dioctyltetramethyldisilazane, diisobutyltetramethyldisilazane,diethyltetramethyldisilazane, N-dipropyltetramethyldisilazane,N-dibutyltetramethyldisilazane,1,3-di(para-tertbutylphenethyl)tetramethyldisilazane;N-trimethylsilylacetamide, N-methyldiphenylsilylacetamide,N-triethylsilylacetamide; tert-butyldiphenylmethoxysilane,octadecyldimethylmethoxysilane, dimethyloctylmethoxysilane,octylmethyldimethoxysilane, octyltrimethoxysilane,trimethylethoxysilane, or octyltriethoxysilane.
 5. Microfibrilsaccording to claim 1, wherein the halogenated alkylating agent is offormula R₄—X, wherein: X is chlorine, bromine or iodine and R₄ is anoptionally substituted, saturated or unsaturated, linear, branched orcyclic hydrocarbonaceous radicals having 1 to 30 carbon atoms. 6.Microfibrils according to claim 5, wherein the halogenated alkylatingagent is chloropropane, chlorobutane, bromopropane, bromohexane,bromoheptane, iodomethane, iodoethane, iodooctane, iodooctae oriodobenzene.
 7. Microfibrils according to claim 1, wherein theisocyanate is of formula R₅—NCO, wherein: R₅ is an optionallysubstituted, saturated or unsaturated, linear, branched or cyclichydrocarbone radicals having 1 to 30 carbon atoms.
 8. Microfibrilsaccoding to claim 7, wherein the isocyanate is butyl isocyanate,tert-butyl isocyanate, pentyl isocyanate, octyl isocyanate, dodecylisocyanate, octadecyl isocyanate or phenyl isocyanate.
 9. Microfibrilsaccording to claim 1, wherein the alkylene oxide is of formula:

wherein: R₆ represents an optionally substituted, saturated orunsaturated, linear, branched or cyclic hydrocarbonaceous radicalshaving 1 to 30 carbon atoms.
 10. Microfibrils according claim 9, whereinthe alkylene oxide is 1,2-epoxybutane, 1,2-epoxyhexane, 1,2-epoxyoctane,1,2-epoxydecane, 1,2-epoxydodecane, 1,2-epoxyhexadecane,1,2-epoxyoctadecane or 1,2-epoxy-7-octene.
 11. Microfibrils according toclaim 1, wherein the glycidyl compound is of formula:

wherein: R₇ represents an optionally substituted, satuared orunsaturated, linear, branched or cyclic hydrocarbonaceous radicalshaving 1 to 30 carbon atoms.
 12. Microfibrils according to claim 11,wherein the glycidyl compound is metyl glycidyl ether, propyl glycidylether, butyl glycidyl ether, 2-methylbutyl glycidyl ether, ethylhexylglycidyl ether, octyl glycidyl ether, lauryl glycidyl ether, allylglycidyl ether or benzyl glycidyl ether.
 13. A process for themanufacture of cellulose microfibrils with a modified surface as definedin claim 1 from cellulose microfibrils obtained by fibrillation of amaterial comprising cellulose fibers, said process comprising the stepsof: i—wetting or dispersing the cellulose microfibrils in a liquiddispersion medium which does not destroy the cellulose microfibrils,ii—adding, to the dispersion, an agent for the etherification or amixture of agents for the etherification of the hydroxyl functionalgroups of the cellulose and optionally a catalyst or an etherificationactivator and carrying out an etherification reaction, said agent beinga silylating agent, isocyanate, halogenated alkylating agent, alkyleneoxide, or glycidyl compound, iii—halting the etherification reactionafter the desired degree of surface substitution (DSS) has beenobtained, and iv—separating the microfibrils obtained in step iii fromthe liquid medium.
 14. A process for viscosifying or texturizing a fluidmedium or a reinforcing filler comprising the step of adding to saidfluid or filler a viscosifying or texturizing amount of microfibrils asdefined in claim
 1. 15. A cosmetic formulation, drilling fluid, paint,glaze, adhesive or ink, comprising a viscosifying amount of microfibrilsas defined in claim
 1. 16. A thermoplastic material thermosettingmaterial, crosslinked elastomer, noncrosslinked elasomer, or masticcomprising a reinforcing amount of microfibrils as defined in claim 1.17. Mirofibrils according to claim 1, wherein the degree of surfacesubstitution (DSS) is between 0.1 and
 1. 18. Microfibrils according toclaim 17, wherein the degree of surface substitution (DSS) is between0.2 and 0.7.